The present invention relates to a communication method and a communication apparatus suitably applicable to a radio telephone apparatus usable as a terminal of a radio telephone system called a personal handy phone system (PHS), for example.
A telephone apparatus called a cordless telephone is configured of a plurality of telephone sets. The cordless telephone includes a base unit connected to a cable telephone line and one or a plurality of handset units for performing a radio communication with the base unit. Each handset unit is adapted to communicate with a telephone set connected to the telephone line through the base unit. Also, some cordless telephone apparatuses permit extension between the base unit and handset units (or extension between a plurality of handset units).
The telephone apparatus configured as such a cordless telephone has comparatively many improved functions offered as conveniences to individual telephone sets. The telephone apparatus has the function of an answering machine, for example, which can automatically answer a call arriving at a person who is not at home. Other telephone apparatus include a plurality of one-touch dial keys for transmitting a message to specific parties in registration to facilitate the transmission to such parties with which the caller has frequent conversations.
A handset unit making up the cordless telephone apparatus is usable as a portable telephone set (hereinafter called a PHS terminal) for a communication network system called the personal handy phone system (PHS). For the PHS, there are located a plurality of base stations arranged at a predetermined spatial interval with each other and connected to the telephone line. Each base station can communicate by a radio wave with PHS terminals existing in a service area of several hundred meters in radius of the particular base station. The PHS terminals located within the service area can transmit a message to an arbitrary party and receive a call from an arbitrary party through the base station.
In the case where a handset unit for the cordless telephone has the function of a PHS terminal, the same scheme is generally employed for the communication with the base station as for the communication with the base unit for the cordless telephone system thereby simplifying the circuit configuration of the handset units.
In this way, the handset units making up the cordless telephone system can be used also as a PHS terminal. As a result, in an indoor operation mode permitting a handset unit to have a communication with the base unit from a home, for example, the handset unit can be used as a cordless telephone set, while in a public mode where it can be used outdoor as a PHS terminal, thus conveniently widening the range of applications as a telephone set.
The handset unit of the cordless telephone system preferably has arranged thereon comparatively many keys to make possible a comparatively complex operation in order to realize multiple functions required as a cordless telephone. A PHS terminal which is routinely carried as a portable telephone, on the other hand, is preferably as small in size and light in weight as possible. In the case where a single terminal is used both as a handset unit of the cordless telephone and a PHS terminal, the process of selection is required for the terminal to have a multiple function as a telephone set of ordinary size or to be reduced in size with a limited function.
It is thought that this inconvenience can be obviated by providing two terminals and selectively using them according to specific applications, one having a multiple function and constructed in a size convenient to use as a handset unit of the cordless telephone system and the other having a size convenient to use as a PHS terminal. In such a case, each of the two terminals is registered in the communication network side as a PHS terminal, and therefore the basic rate covering two units is required to be paid. The user, therefore, is burdened with an increased cost. Also, since each PHS terminal is basically assigned a different telephone number, the two telephone sets have different telephone numbers. It is thus inconveniently impossible for the two terminals to serve a single call arriving in the PHS mode at the same time.
Further, in view of the fact that the PHS terminal is generally configured in a small size and carried by a user, it is liable to be lost or stolen when the user is out with the PHS terminal. For example, a third party who picked up the lost PHS terminal may abuse it (i.e., a person other than the owner of the PHS terminal may use it for communication with other parties). Under the present circumstances, no means is available for preventing such an abuse.
As the radio telephone system, there is available such a system in which personal identification information such as a telephone number, an identification code and so on are stored in an IC card, and a terminal having the IC card mounted thereon functions as a telephone set assigned the particular telephone number. In this system, the IC card is mounted on a small-sized portable terminal on one occasion, and the IC card is mounted on a multiple-function terminal on another occasion, thereby making it possible for a plurality of terminals to share the same telephone number and to use it. Even in such a system, however, the problem still remains that the IC card may be abused by a third party when it is lost or stolen.